Method of pretreating bands and sheets of steel for one-layer enameling, and electrolytic bath for use in connection therewith

ABSTRACT

A method of electrochemically pretreating articles, especially bands and sheets of steel, for a later one-layer enameling process according to which the article to be pretreated is degreased and, if necessary, pickled and in an electrolytic nickel and/or cobalt bath containing a nitrate ion is provided with a nickel and/or cobalt layer.

United States Patent J iirging et al.

[451 Apr. 29, 1975 METHOD OF PRETREATING BANDS AND SHEETS OF STEEL FORONELAYER ENAMELING, AND ELECTROLYTIC BATII FOR USE IN CONNECTIONTIIEREWITII Inventors: Klaus Jiirging, Remscheid; Hans Zwach, Wuppertal,both of Germany Assignee: Hoeschst Aktiengesellschaft,

Dortmund, Germany Filed: Oct. 4, 1972 Appl. No.: 295,010

Foreign Application Priority Data Oct. 6, 1971 Germany 2149808 Sept. 2,1972 Germany 2243339 US. Cl. 204/34; 204/48; 204/49 Int. Cl. C23b 5/48;C23b 5/08; C23d 5/00 Field of Search 204/34, 48, 49

Primary ExaminerF. C. Edmundson Attorney, Agent, or FirmWalter Becker[57] ABSTRACT A method of electrochemically pretreating articles,especially bands and sheets of steel, for a later onelayer enamelingprocess according to which the article to be pretreated is degreasedand, if necessary, pickled and in an electrolytic nickel and/or cobaltbath containing a nitrate ion is provided with a nickel and/or cobaltlayer.

5 Claims, No Drawings METHOD OF PRETREATING BANDS AND SHEETS OF STEELFOR ONE-LAYER ENAMELING, AND ELECTROLYTIC BATH FOR USE IN CONNECTIONTHEREWITH The present invention relates to a method of electrochemicallypretreating bands and sheets of steel and articles made therefrom forthe one-layer enameling process according to which the bands and sheetsare degreased, if desired pickled, and in an electrolytic nickel and/orcobalt bath are provided with a nickel and/or cobalt layer.

Methods of one-layer enameling steel sheets, for instance methods inwhich no base enamel is employed, have become known. According to one ofthese known methods, the metal sheet to be enameled is firstelectrolytically degreased and after washing in water is pickledchemically or electrolytically in sulfuric acid or in a mixture offormic acid and nitric acid, and subsequently is rinsed again.

Following the pickling step, the sheet metal is plated electrolyticallywith nickel in a nickel bath and subsequently is enameled. If theenameling process is not carried out shortly after the nickel platingstep, the metal sheet to be nickel plated is electrolytically coatedwith a zinc layer which is removed prior to the enameling process. Asufficient adherence between the steel metal sheet and the enamel coatis, however, not obtained by this method.

According to a further heretofore known method of enameling metalsheets, likewise an electroplating of the metal sheet with nickel issuggested which is annealed in an oxidizing manner and is subsequentlypickled. lnstead of nickel, also cobalt or a mixture of nickel andcobalt may be used. The oxidizing annealing at relatively hightemperatures and subsequent cooling off in a certain definite atmosphereis, however, relatively expensive and requires considerable equipment sothat also this known method is not fully satisfactory.

According to still another heretofore known method, the metal sheet islikewise cleaned, washed and briefly treated with an acid. Thereuponfrom a chemical bath, a nickel and/or cobalt layer is deposited upon themetal sheet, whereupon the sheet is rinsed, is heated in an oxidizingatmosphere, and zinc is deposited upon the nickel and/or cobalt layerwhich zinc is again removed by the user or in the enameling plant. Thedrawback of this known method, similar to the before mentioned method,consists in the necessary oxidizing annealing, on the one hand, and, onthe other hand, in the fact that the baths to be employed are as totheir composition rather unstable. ln addition thereto, this method aswell as the other heretofore known methods will operate satisfactorilyonly when the surface of the metal sheets to be enameled are roughenedby the removal ofa certain quantity of material from the steel surfacewhich quantity is generally within the range of from to 40 gr/mFurthermore, with this and other known methods, the time required is toolong to be able economically to carry out a continuous method for thepretreatment involved. Therefore, aside from a few exceptions, theseknown methods have not been adopted in practice to any material extent.

It is, therefore, an object of the present invention to provide a methodof the above described general character by means of which it will bepossible in a very simple manner to pretreat bands or sheets to beenameled in a continuous way, while at the same time the methodaccording to the present invention will be such that it can be practicedand controlled in a simple manner so that also the requiredinstallations for carrying out the method can be kept simple.

It is a further object of the present invention further to simplify andimprove the method set forth in the preceding paragraph whilesimultaneously improving the adherence of the enamel layer applied afterthe pretreatment.

These and other objects and advantages of the inven-- tion will appearmore clearly from the following specification in connection with thevarious examples set forth further below.

In deviation from the heretofore adopted theory and practice forpretreating bands and sheets of steel for the subsequent enameling step,according to which it was always necessary to pickle the bands andsheets by a measurable removal of metal prior to the application of themetallic intermediate layers of nickel and/or cobalt to be able toprovide a sufficiently good adherence of the enamel coat, the objects ofthe present invention as set forth above have been realized by addingnitrate ions to the nickel and/or cobalt bath. According to oneadvantageous method of practicing the present invention, there are addedto the nickel and/or cobalt bath from 0.5 to 110 gr, preferably from 25to gr, of nitrate ions per liter of electrolyte liquid, and a nickeland/or cobalt layer is at room temperature deposited on the band orsheet in a time period of from 50 to seconds at a current density offrom 5 to 15 amperes/dm at a pH-value of the electrolyte of from 1 to 5.In an advantageous and simple manner, the electrolytic bath for carryingout the method according to the invention consists of from 20 togr/liter of nickel, 0.6 to gr/liter of ammonium nitrate, from 15 to 40gr of boric acid in sulfuric acid or hydrochloric acid solution. lf anintermediate or adhering layer consisting merely of cobalt is to bedeposited on the sheet or band, the bath expediently consists of from 20to 100 gr/liter of cobalt, of 0.6 to 135 g/liter of ammonium nitrate, offrom 15 to 40 gr/liter of boric acid in sulfuric acid solution. lf anadhesive layer consisting of nickel and cobalt is required for thesubsequent enameling step, a corresponding mixed bath is employed inconformity with the above referred to bath compositions.

According to a further development of the invention, the nickel and/orcobalt layer is in a time period of from 5 to 60 seconds deposited at acurrent density of from 5 to 50 A/dm in the bath having a temperature offrom room temperature to boiling temperature. In this way a considerablywidened range of the bath temperature and, more specifically, from roomtemperature or slightly above room temperature to boiling temperature ofthe bath, is available and a further reduced time range of from 5 to 15or 14 seconds, and furthermore a likewise widened range of the currentdensity of from 15 or 16 to 50 A/dm is available in an advantageousmanner for carrying out the method according to the invention.

The method according to the invention will now be explained inconnection with the following examples.

EXAMPLE 1 a. Electrolytic degreasing in alkaline lye at 80C for 6seconds. b. Rinsing for 5 seconds.

c. Pickling at room temperature in a 10% by weight sulfuric acid for 2seconds.

d. Rinsing for seconds.

e. Nickel plating in an electrolyte having the following composition:135 gr/liter of nickel sulfate 35 gr/liter of ammonium nitrate 25gr/liter of boric acid in a sulfuric acid solution at a pH-value of 3.5and at room temperature, a current density of A/dm in 28 seconds.

f. Rinsing for 5 seconds.

g. Drying.

EXAMPLE 2 The method is carried out in the same manner as set forth inExample 1 without the method step cpickling while the method stepb-rinsing is replaced by a spray rinsing step with longer duration ofthe spraying.

EXAMPLE 3 The method steps a) to d) and f) and g) of Example 1 arelikewise used in this Example. As method step e) there will be carriedout a coating or plating with cobalt in an electrolyte composed of 135gr/liter of cobalt sulfate 35 gr/liter of ammonium nitrate 30 gr/literof boric acid, and this is carried out in a sulfuric acid solution at apH- value of 3.5 and at room temperature, and a current density of 10A/cm in 28 seconds. Method step c) may also in this Example be replacedin the same manner as described in connection with Example 2.

EXAMPLE 4 a. Electrolytic degreasing in alkaline lye at 80C for 6seconds. b. Rinsing for 5 seconds. c. Pickling at room temperature in a10% by weight sulfuric acid for 2 seconds. (1. Rinsing for 5 seconds. e.Nickel plating in an electrolyte having the following composition: 135gr/liter of nickel sulfate 35 gr/liter of ammonium nitrate 25 gr/literof boric acid at a pH-value of 4.5, a temperature of from 40 to 60 C,and a current density of 20 A/dm in 28 seconds.

f. Rinsing for 5 seconds. g. Drying.

EXAMPLE 5 The method steps a) to d) and f) and g) of Example 4 areapplied to this Example. The nickel plating according to method step e)in Example 4 is carried out with the same electrolyte but at a pH-valueof 5.0, a temperature of from 10 to 25C, and a current density of 30A/dm for 20 seconds.

EXAMPLE 6 This Example follows the same method steps a) to d) and f) andg) as in Example 4. The nickel plating according to method step e) iscarried out with the same electrolyte but at a pH-value of 4.0, atemperature of from 80 to 90C, and a current density of A/dm for 45seconds.

EXAMPLE 7 The method steps a) to d) and f) and g) of Example 4 alsoapply to this Example. The nickel plating according to the method stepe) of Example 4 is carried out with the same electrolyte as in Example 4but at a pH- value of 4.5, a temperature of from to C, and a currentdensity of 40 A/dm for 10 seconds.

With all of the pre-treatments set forth in the above Examples,following the one-layer enameling carried out in a manner known per se,a firmly adhering enamel layer is obtained.

As will be evident from the above, the advantages of the methodaccording to the present invention, in addition to avoiding oxidizingannealing steps and an acid treatment of relatively long duration,consist primarily in the simple way of carrying out and controlling thecourse of the method according to the invention. In view of this simpleway of carrying out the method according to the invention,correspondingly simple installations for carrying out the method areobtained which method can also be practiced in installations already inexistence. lnasmuch as in conformity with the method of the inventionthe heretofore required acid treatment of the metal sheets and bands isno longer necessary, the method according to the invention also avoidsthe problems of waste water refining which problems occur to an everincreasing extent. Furthermore, with bands and sheets pretreated inconformity with the present invention, it is no longer necessary toapply a protective layer against deformation, for instance a zinc layer,because the adhering layer applied to the material during thepre-treatment cannot be mechanically damaged. The adherence of theone-layer enamel coat on the material pretreated in conformity with themethod of the present invention, for which material there may beemployed steel with carbon contents of up to 0.10% and also steel whichhas been previously subjected to a decarborization, is extremely good sothat the method of the invention may be employed in a wide field.

According to the improved method of the invention, it is no longernecessary to cool the electrolyte. Moreover, the method according to theinvention also improves the interengagement of the enamel coat with thesupporting or base material, the bands. sheets or individual articles ofsteel is improved so that an excellent adherence is obtained.

It is, of course, to be understood that the present invention is by nomeans limited to the specific examples set forth above but alsocomprises any modifications within the scope of the appended claims.

What we claim is:

1. A method of pretreating a steel article for an enameling process,which includes the steps of preparing an electrolyte bath containing atleast one element selected from the group consisting of nickel andcobalt, adding non-substituted nitrate ions from inorganic substance tosaid electrolyte in the amount of 0.5 to l 10 gr./liter of theelectrolyte fluid, and depositing upon the steel article a layercontaining at least one of said elements from the electrolyte bath uponthe article to be pretreated at a bath temperature of from roomtemperature to boiling temperature at a current density of from 5 to 50A/dm for a period of from 5 to 60 secends.

2. A method in combination according to claim l, which includes the stepof pickling the article to be' gr/liter of nickel, from 0.6 to 135gr/liter of ammonium nitrate and from 15 to 40 gr/liter of boric acid ina solution selected from the group consisting of sulfuric acid solutionand hydrochloric acid solution.

5. A method in combination according to claim 1, in which theelectrolytic bath contains from 20 to gr/liter of cobalt, from 0.6 togr/liter of ammonium nitrate and from 15 to 40 gr/liter of boric acid insulfuric acid solution.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO. Dated 9Invent0r(s) Klaus Jur'ging et 211.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby'corrected as shown below:

On the Cover Sheet, in item "Hoesohst" should read Hoesoh Signed andScaled this twenty-first D ay Of October 1975 [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner uf'Parenlsand Trademarks

1. A METHOD OF PRETREATING A STEEL ARTICLE FOR AN ENAMELING PROCESS,WHICH INCLUDES THE STEPS OF PREPARING AN ELECTROLYTE BATH CONTAINING ATLEAST ONE ELEMENT SELECTED FROM THE GROUP CONSISTING OF NICKEL ANDCOBALT, ADDING NON-SUBSTITUTED NITRATE IONS FROM INORGANIC SUBSTANCE TOSAID ELECTROLYTE IN THE AMOUNT OF 0.5 TO 110 GR./LITER OF THEELECTROLYTE FLUID, AND DEPOSITING UPON THE STEEL ARTICLE A LAYERCONTAINING AT LEAST ONE OF SAID ELEMENTS FROM THE ELECTROLYTE BATH UPONTHE ARTICLE TO BE PRETREATED AT A BATH TEMPERATURE OF FROM ROOMTEMPERATURE TO BOILING TEMPERTURE AT A CURRENT DENSITY OF FROM 2 TO 50A/DM2 FOR A PERIOD OF FROM 5 TO 60 SECONDS.
 2. A method in combinationaccording to claim 1, which includes the step of pickling the article tobe treated prior to electrolytically depositing thereon a layer of atleast one of said elements.
 3. A method in combination according toclaim 1, which includes the step of depositing upon the article to betreated the layer containing the respective element at room temperaturewithin a period of from 15 to 60 seconds at a current density of from 5to 15 A/dm2 and at a pH-value of the electrolyte of from 1 to
 5. 4. Amethod in combination according to claim 1, in which the electrolytebath contains from 20 to 100 gr/liter of nickel, from 0.6 to 135gr/liter of ammonium nitrate and from 15 to 40 gr/liter of boric acid ina solution selected from the group consisting of sulfuric acid solutionand hydrochloric acid solution.
 5. A method in combination according toclaim 1, in which the electrolytic bath contains from 20 to 100 gr/literof cobalt, from 0.6 to 135 gr/liter of ammonium nitrate and from 15 to40 gr/liter of boric acid in sulfuric acid solution.